Treating alum



Patented Sept. 10, 1940 4 'UNITED STATES PATENT OFFICE j No Drawing. Application September 11, 1939,

Serial No. 294,271

'I-Ghims.

(Granted under the act of March 3, 1883, as

amended April 30,

The invention herein described may be manufactured and used by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This invention relates to the treatment of alums and particularly their partial dehydration. One of the objects of this invention is to provide a process for the rapid partial dehydration of alums. Another object of this invention is to partially dehydrate alum so that it may be subsequently completely dehydrated or desulfurized either continuously or discontinuously without the danger of the material adhering to the walls of the furnace. Other objects of this invention include the provision for an improvement in the process of producing aluminum oxide starting with the treatment of aluminum ore with sulfuric acid.

- The problem of dehydrating alums has been no long known in connection with the production of aluminum oxide involving the treatment of aluminum ores, particularly those also containing potassium and other alkali metal compounds, with sulfuric acid. Notwithstanding the fact that Bl it is theoretically possible to merely say that the normal alum resulting from such treatment is dehydrated and calcined, nevertheless, as a practical matter, alums so treated directly fuse, become partially dehydrated and then solidify 80 on the walls of the furnace, whether it be continuous or discontinuous, and thereafter may not be removed except with extreme difliculty. Of the numerous proposals which have been made to solve this problem the following are the most characteristic: either to convert the normal potassium alum into a basic alum which does not evidence this undesirable characteristic when heated or to partially dehydrate the normal alum at a temperature below its melting point.

I have discovered an eifective and rapid method for dehydrating solutions containing normal alum, or partially dehydrating normal alums if they already occur in the solid form, so that the alum may be subsequently either completely dehydrated or desulfurized without fusion, by

heating the solution or the alum to a temperature just above the melting point of the alum until the water content of the residue is such that the fluid alum discharged from the heating zone so readily solidifies and the solidified alum will not fuse when subsequently heated.

One example of the operation of my process is given for the partial dehydration of pure normal potassium alum. A charge of 948 parts by weight of the normal potassium alum was placed in an evaporator. The charge was heated to a temperature of 100 0., which is just above the melting point for pure potassium alum containing 24 mols of water, namely, 92 C. The heating of the fluid mass was continued until a residue 5 of 818 parts by weight, corresponding to 16.8 mols of water for each mo] of anhydrous alum, remained in the evaporator. The liquid was then chilled and the resulting solid mass crushed. The crushed material was heated rapidly to a tem- 1o perature of 400 C. to substantially completely dehydrate it. Particular attention was given to the observation as to whether or not the partially dehydrated material was completely fluid or tended to solidify in the evaporator and as to 15 whether the crushed product, on subsequent heating, showed evidence of fusing or at least softening suiliciently to adhere to the walls of the furnace in which it was heated, difllcult, if not practically impossible, to readily remove the same. The operation was repeated in all details except that, in this instance, a residue of 803 parts by weight, corresponding to 15.7 mols of water for each mol of anhydrous alum, remained in the evaporator. The operation was again repeated in all the preliminary details except that, in this instance, a residue of 786 parts by weight, corresponding to 15 mols of water for each moi of anhydrous alum, remained in the evaporator. At the end of this latter operation, however, the product hardened in the evaporator and could not be removed as liquid. The results obtained are summarized as follows: 7

(a') 16.8 mols H20/mol anhydrous alum adhered to furnace walls when subsequently heated (b) 15.7 mols'I-IzO/mol anhydrous alum satisfactory (c) 15.0 mols HaO/mol anhydrous alum set up solid in evaporator Another example for the operation of my process is given for the partial dehydration of mixed alum obtained from alunite. A charge of 25.5 parts by weight of calcined alunite was digested with 74.5 parts by weight of sulfuric acid, containing 30% by weight of H2804, to produce a solution containing primarily A12(SO4)3, mSOa NazS04 and Fen-SO03. An amount of potassium sulfate required to produce essentially potassium alum from M20804): contained in the solution, 12,4 parts by weight, was added to the solution. This solution also contained some sodium alum and a trace of iron alum. The solution was charged into an evaporator and heated to a temperature of 100 C. The heating of the fluid mass was continued until a residue of 84.0 parts by weight, corresponding to 17.9 mols of water for each mol of anhydrous alum, remained in the evaporator. The liquid was then chilled and the resulting solid mass crushed. The crushed mass was heated rapidly to a temperature of 400 C. to substantially completely dehydrateit. Particular attention was again given to the observation as to whether or not the partially dehydrated material was completely fluid or tended to solidify in the evaporator and as to whether the crushed product, on subsequent heating, showed evidence of fusing or at least softening suiflciently to adhere to the walls of the furnace in which it was heated, thereby making it diflicult, if not practically impossible, to readily remove the same. The operation was repeated in all details except, in this instance, a residue of 82.5 parts by weight, corresponding to 17.2 mols of water for each mol of anhydrous alum, remained in the evaporator. The operation was again repeated in all the preliminary details except, in this instance, a residue of 79.6 parts by weight, corresponding to 15.7 mols of water for each mol of anhydrous alum, remained in the evaporator. At the end of this latter operation, however, the product hardened in the evaporator and could not be removed as liquid. The results obtained are summarized as follows: (a) 17.9 mols HaO/mol anhydrous alum adhered to furnace walls when subsequently heated (b) 17.2 mols HaO/mol anhydrous alum satisfac- 1 1'? (c) 15.7 mols HaO/mol anhydrous alum set up solid in evaporator It is evident that there are numerous factors which will influence conditions for the most satisfactory operation of my invention, the actual limits of which cannot be established except by a detailed study of each set of raw materials and the intermediate and finished products involved.

The alum which is to be partially dehydrated may be any normal alum which, in the crystalline form, contains 24 mols of water for each mol of anhydrous alum or mixture of such alums. The more common sodium and potassium alums have been found to be effectively treated by my process but the alums derived from the less common alkali metals may be equally suitable for treatment by this process.

The alums used may be of intermediate as well. as high states of purity and the starting material may be in solution as well as in the solid form. In some instances it may be desirable to dissolve the solid in a minimum amount of water prior to the direct dehydration operation.

The temperature to which the alum or the solution of alum is heated to effect partial dehydration will depend upon the composition of the alum or mixed alum but, in any event, is just above the melting point of the alum or alums containing water corresponding to 24 mols of water for each mol of anhydrous alum. The temperature maintained as the heating is continued is such that the alum still exists in a fluid state.

The extent of the partial dehydration will vary somewhat with the composition of the alum, as shown in the examples given above, where a prodnot containing 15.7 mols of water for each mol of anhydrous alum, obtained from pure potassium alum, was satisfactory and where a product containing 17.2 mols of water for each mol of an,- hydrous alum obtained from mixed alum from alunite was satisfactory. The extent of the amount of water which may be left in the par- 'tially dehydrated alum row limits. with the lower limit being that amount falls 'wahiii. critical as which will permit the alum to be discharged the upper to be subsequently heated without fusion, or at least without suflicient softening to permit the material so heated to adhere to the walls of the furnace in which it is heated.

It will be seen, therefore, that this invention may be actually carried out by the modification of certain details without departing from its spirit and scope.

I claim:

1. Process of treatinga solution of mixed alum. obtained by digesting calcined alunite with sulfuric acid and adding an amount of potassium sulfate required to produce essentially potassium alum, so that the alum may be subsequently either completely dehydrated or desulfurized without fusion, which comprises heating the solution of alum to a temperature Just above the melting point of the alum containing 24 mols of water for each mol of alum; continuing the heating of the fluid alum until the residue contains substantially 17 mols of water for each molof anhydrous alum; discharging the fluid alum fronfi the heating zone; cooling the fluid as discharged until it solidifies; and further dehydrating the sblidifled alum.

from the heating zone; cooling the fluid as dis-- charged until it solidifies; and further dehydrating the solidified alum.

3. Process of treating a normal potassium alum, so that the alum may be subsequently either completely dehydrated or desulfurized without fusion, which comprises heating the alum to a temperature just above the melting point of the alum; continuing the heating of the fluid alum until the residue contains substantially 16 mols of water for each mol of anhydrous alum; discharging the fluid alum from the heating zone; cooling the fluid as discharged until it solidifies; and further dehydrating the solidified alum.

4. Process of treating an alum from the class consisting of normal sodium and potassium alums that the alum may be subsequently either completely dehydrated or desulfurized without fusion, which comprises heating the .alum to a temperature just above the melting point of the alum; continuing the heating of the fluid alum 1 2,214,214 alum discharged from the heating zone readily solidifies, and the solidified alum will not fuse when subsequently heated; discharging the fluid alum from the heating zone; cooling the fluid alum so discharged until it solidifies; and further dehydrating the solidified alum.

6. Process of treating normal potassium alum, so that the alum may be subsequently either completely dehydrated or desulfurized without fusion, which comprises heating the alum to a temperature just above the melting point of the alum; continuing the heating of the fluid alum until the water content of the residue is such that it contains substantially l6 mols of water for each mol of anhydrous alum, a composition such that the fluid alum discharged from the heating zone readily solidifies, and the solidified alum will not fuse when subsequently heated; discharging the fluid alum from the heating zone; cooling the fluid alum so discharged until it solidifies; and further dehydrating the solidified alum.

'7. Process of treating a solution of mixed alum,

obtained by digesting calcined alunite with sulfuric acid and adding an amount of potassium sulfate required to produce essentially potassium alum, so that the alum may be subsequently either completely dehydrated or desulfurized without fusion, which comprises heating the solution of alum to a temperature just above the melting point of the alum containing 24 mols of water for each mol of anhydrous alum; continuing the heating the fluid alum until the water content of the residue is such that it contains substantially 17 mols of water for each mol of anhydrous alum, a composition such that the fluid alum discharged from the heating zone readily solidifies, and the solidified alum will not fuse when subsequently heated; discharging the fluid alum from the heating zone; cooling the fluid alum so discharged until it solidifies; and further dehydrating the solidified alum.

JOHN H. WALTHAIL.

CERTIFICAUE OF CORRECTION Patent No. 2,'21L;,21l;. September 10, 191p.

JOHN H. wALTHALL.

It is hereby certified that error appears in the printed specificetion of the above numbered patent requiring correction as follows: Rage 1, sec ond column, line 50', for "A1 (SOh) read --Al SO1 page 5, second column, line 11, claim'], after "heating" insert --of--; andthat the said Letters Patent aho'dld be read with this correction therein that the same may conform to the record of the case lathe-Patent Office. Signed and aealed'thia lsth-ddy'of October, A.' D. 19 40.

Henry Van Aradal'e, (Seal) Actingfiommieeioner of Patents. 

